Hereinafter, a method for manufacturing a related CMOS image sensor will be briefly described. A field insulating layer is formed over a silicon substrate in order to electrically insulate devices from each other. Next, light detectors such as photodiodes are formed, and then an inter-layer dielectric layer and a metal interconnection layer are formed. Thereafter, protection layers such as a passivation oxide layer and a passivation nitride layer are deposited in order to protect devices or a pad from moisture or physical shocks such as scratches. Subsequently, a color filter array is formed to detect color images, and a micro-lens array is formed over the upper part of the color filter array. The color filter array process, the planarization process, and the micro-lens process all include a photoresist coating process. Thus, if a process for protecting a pad is not employed, many problems may occur.
Problems relative to methods for manufacturing the related CMOS image sensor will be described with reference to FIGS. 1A to 1F. FIGS. 1A to 1F are sectional views showing a process of forming a pad and a pad protection layer of a CMOS sensor, a micro-lens process, and a stripping process for the pad protection layer.
As shown in FIG. 1A, a thick passivation oxide layer 110 is deposited over the pad 100 in order to protect the pad 100. A chemical mechanical polishing (CMP) process is performed to planarize the passivation oxide layer 110. A thick passivation nitride layer 120 is formed over the resultant structure, thereby forming a first pad protection layer. Thereafter, a photolithography process is performed with respect to the passivation oxide layer 110 and the passivation nitride layer 120, thereby exposing a pad.
Next, FIG. 1B is a sectional view showing a process of depositing a thin plasma enhanced-tetra ethyl ortho silicate (PE-TEOS) layer or a thin thermo-setting resin layer over the passivation nitride layer 120 as a second pad protection layer 130. A color filter array process, a planarization process, and a micro-lens process, which are the subsequent processes, include a photo process. In this case, the second pad protection layer 130 protects the pad during the photo process. If the PE-TEOS layer is used as the second pad protection layer 130, since an adhesive force between the photoresist and the PE-TEOS layer is inferior, a peeling phenomenon occurs in a color filter. If the thermo-setting resin layer is used as the second pad protection layer 130, since both the thermo-setting resin layer and the photoresist have the same components, an adhesive force between the thermo-setting resin layer and the photoresist is superior. Accordingly the peeling phenomenon is prevented in the color filter. However, if the processes are reworked due to errors occurring in the color filter array process, solvent cleaning is performed in order to strip the photoresist. At this time, the thermo setting resin layer is stripped with the photoresist. Thereafter, a thermo-setting resin layer is deposited, and then a color filter array process is performed again. However, since the solvent cleaning is performed in a state in which the pad 100 is exposed, pad corrosion or pad contamination may be caused. If such pad contamination is caused, the yield rate of wafers and semiconductor packages is reduced when a probe test is performed.
FIG. 1C is a sectional view showing a process of forming a blue/green/red color filter array 140 over the first pad protection layer through a color photo-process. FIG. 1D is a sectional view showing a process of forming a planarization layer 150 through a photo-process for a planarization layer. In addition, FIG. 1E is a sectional view showing a process of forming a micro-lens 160 over the planarization layer 150. The processes include several photo-processes, and a process for forming the micro-lens 160 includes a thermal reflow process involving heating a semiconductor substrate in order to form a convex micro-lens.
FIG. 1F is a sectional view showing a process of removing the second pad protection layer 130 after forming the micro-lens 160. If the PE-TEOS layer serves as the second pad protection layer, the second pad protection layer is removed through a dry etching process using plasma. If the thin thermo-setting resin layer serves as the second pad protection layer 130, the second pad protection layer is removed through oxygen ashing.